In many rotary grinding apparatuses, the annular breaker rings and the center shaft of the rotor assembly are interconnected by elongate shear pins located within bores that extend radially through the outer and inner circumferential surfaces of the breaker rings and a considerable distance into the center shaft of the rotor. Customarily a plurality (e.g., three) of such pins are associated with each breaker ring. A fourth radial bore containing a breakable cylinder of lubricant such as oil may also be provided in association with each breaker ring and the shaft. When a blockage within the apparatus prevents a breaker ring from rotating in unison with the shaft, the shear pins and oil cylinder associated with such ring break, permitting relative rotative movement between the shaft and ring. The released oil assists in preventing galling or other damage to the abutting and then relatively moving surfaces of the breaker ring and the shaft. Such damage is particularly like to occur when cessation of the breaker ring's rotation is not promptly detected, and the grinding apparatus continues in operation. When the malfunction is detected and operation of the apparatus is halted, new shear pins and a new oil cylinder must be substituted for the broken ones. Removal of the broken shear pins, and particularly the portions thereof located within the shaft of the apparatus, is frequently quite difficult. To facilitate their removal, the pins may be of an internally threaded tubular type adapted to receive an externally threaded tool. If a threaded connection can be established between the pins and the tool, which is not always the case, the tool may be used to attempt to pull the broken portion of the shear pins outwardly from the shaft. Alternatively or additionally, a smaller diameter shaft bore communicating and aligned with the inner end of that containing the shear pin may be provided for the purpose of receiving a set screw or other "jacking" device by which the broken shear pin may be pushed outwardly from the shaft. Even with the assistance of such devices, however, removal of the broken shear pins normally is a tedious and time-consuming task. Additionally, even after the broken shear pins are removed, difficulties may be encountered in aligning the substitute replacement pins with the bores in the rotor shaft, particularly if the bores have been damaged or if metal from the broken shear pins has been transferred onto the shaft during continued operation of the apparatus following breakage of the pins. The foregoing factors greatly increase the down-time and maintenance costs of the grinding apparatuses.